1. Field of the Invention
The present invention relates to the field of electrical connectors, and in particular to a miniaturized Universal Serial Bus (USB) connector socket, such as a Micro-B USB socket, and providing therein thermally-coupled over-current and over-voltage circuit protection elements.
2. Introduction to the Invention
Standardized plug and socket connectors are widely employed in the electrical and electronic arts. One example, the Universal Serial Bus (USB), is a widely recognized and followed connectivity specification that was first developed in 1995 by technology companies. The USB specification provides an interconnect mechanism which includes transfer of serial data as well as operating power via standard form electrical connectors. By the USB specification a USB-compliant power supply will provide a peripheral device with a fixed voltage in a range of 4.75 and 5.25 Volts with current of at least 0.5 Amperes. The USB specification has evolved with the general trend toward electronic circuit miniaturization, and has specified a Mini-B USB connector plug and socket to handle miniature peripheral devices such as digital cameras, PDAs, and hand-sets, for example; see USB 2.0 Specification ECN #1: Mini-B Connector, Oct. 20, 2000. More recently the even smaller Micro-B USB connector plug and socket have been proposed.
While USB has provided ease of use, expandability, and speed for the end user and has resulted in widespread adoption and use in countless personal computing, consumer electronics, and mobile devices, the success of this standard has increased the likelihood of over-voltage/over-current electrical fault conditions. Electrical faults are known to occur, making unprotected downstream electronics devices susceptible to damage. Typical over-voltage/over-current faults include inductively induced voltage spikes, voltage spikes from intermittent connections (defective cords or dirty/corroded contacts) and/or over-voltage charger connections resulting from component failure or user error (plugging in the wrong charging unit, for example). Less typical but possible faults include reversal of voltage supply polarity. Because USB has become such a ubiquitous power-charging interface, some vendors have supplied AC to DC converters with a USB output connector. These converters may have unknown, inadequate, or non-existent voltage regulation and transient-suppression characteristics. Unprotected devices may be damaged by over-voltage/over-current conditions when connected to such unregulated converters having standardized connectors, such as a USB connector plug. While the USB standard strongly recommends inclusion of an over-current protection element, such as a fuse, as part of each peripheral appliance having a USB connector socket, separate over-current protection elements take up printed circuit board space and may not be conveniently accessed by the user for replacement or reset. Examples of USB connector sockets may be found in U.S. Pat. No. 6,217,378 (Wu) for “Universal Serial Bus Connector”, and U.S. Pat. No. 6,217,389 (Jatou) for “Universal Serial Bus Connector with Integral Over-current Protection Device and Indicator”. While the Jatou '389 patent suggests including a resettable fuse within a USB connector socket, there is no teaching or suggestion as to how one might effectively combine thermally-coupled over-voltage and over-current protection elements within a USB connector socket, much less a much smaller Micro-B USB connector socket.
Discrete over-voltage and over-current protection elements for electrical circuits are well known. Known over-voltage circuit protection elements include reverse avalanche breakdown diodes, zener diodes, transient voltage suppression diodes, thyristors, multilayer varistors, gas plasma ionization devices, and Schottky diodes, whether alone or combined with other circuit elements such as pass transistors and operational amplifiers, for example. Known over-current circuit protection elements include metallic fuses, thermally activated circuit breakers, and thermistors. As used herein, the term “thermistor” includes resistors which vary in resistance as a function of temperature. One known example of an over-current protection element is the polymeric positive temperature coefficient (PPTC) thermistor.
Devices exhibiting a positive temperature coefficient of resistance effect are well known and may be based on certain ceramic materials, e.g., barium titanate, or conductive polymer compositions comprising a polymeric matrix component and a particulate conductive filler material dispersed within the polymer matrix. At relatively low, ambient temperatures the PPTC thermistor has a low electrical resistance, on the order of a few Ohms or less. However, when the PPTC thermistor is exposed to a high temperature resulting from ohmic heating, for example, the polymeric matrix expands and separates the conductive particulates, resulting in a very high electrical resistance, often by as much as five or more orders of magnitude greater than the low temperature resistance. The temperature at which the PPTC thermistor transitions from low resistance to high resistance is known as the switching or “trip” temperature, Ts. When the PPTC thermistor cools to a temperature below the trip temperature, Ts, the polymeric matrix solidifies and shrinks, thereby returning the device to its low-resistance state. When used as an in-series over-current protection device, the PPTC thermistor is referred to as being “resettable”, in that it trips to high resistivity when heated to the switching temperature, TS, thereby decreasing current flow through the protected circuit. When the over-current condition is removed, the PPTC thermistor automatically resets to low resistivity when it cools to below Ts, thereby restoring a low ohmic path enabling full current flow through the protected circuit when electrical power is reapplied thereto.
By “PPTC” is meant a composition including a polymeric matrix and having an R14 value of at least 2.5 and/or an R100 value of at least 10, and it is preferred that the composition should have an R30 value of at least 6, where R14 is a ratio of resistivities at the end and beginning of a 14° C. range, R100 is a ratio of resistivities at the end and beginning of a 100° C. range, and R30 is a ratio of resistivities at the end and beginning of a 30° C. range. Generally, the compositions used in PPTC thermistor elements of the present invention show increases in resistivity which are much greater than these minimum values.
Suitable conductive polymer compositions and elements, and methods for producing the same, are disclosed for example in U.S. Pat. No. 4,237,441 (van Konynenburg et al.), U.S. Pat. No. 4,545,926 (Fouts et al.), U.S. Pat. No. 4,724,417 (Au et al.), U.S. Pat. No. 4,774,024 (Deep et al.), U.S. Pat. No. 4,935,156 (van Konynenburg et al.), U.S. Pat. No. 5,049,850 (Evans et al.), U.S. Pat. No. 5,250,228 (Baigrie et al.), U.S. Pat. No. 5,378,407 (Chandler et al.), U.S. Pat. No. 5,451,919 (Chu et al.), U.S. Pat. No. 5,747,147 (Wartenberg et al.) and U.S. Pat. No. 6,130,597 (Toth et al.), the disclosures thereof being expressly incorporated herein by reference thereto.
It is known to provide planar PPTC thermistors in electrical connection and thermal contact with electronic components such as zener diodes, metal oxide semiconductor field effect transistors (MOSFETs), and more complex integrated circuits forming voltage/current regulators, as exemplified by the teachings and disclosures set forth in commonly assigned U.S. Pat. No. 6,518,731 (Thomas et al.) (particularly FIGS. 45-47), the disclosure thereof being expressly incorporated herein by reference thereto. Also, see, for example, U.S. Pat. No. 3,708,720 (Whitney et al.), U.S. Pat. No. 6,700,766 (Sato) and U.S. Patent Publication 2004/0275046 (Morimoto et al.). While shunt protectors such as semiconductors and series protectors such as PPTC thermistors simultaneously respond to excessive electrical energy, one reason for combining semiconductor circuit protection devices with PPTC thermistors is that the semiconductor devices respond to over-voltage conditions at electronic speeds in microsecond ranges, whereas PPTC thermistors operate relatively much more slowly in reaching the switching temperature, TS, generally measured in milliseconds. By thermally coupling the semiconductor device to the PPTC thermistor, heat first generated in the semiconductor device is rapidly transferred to the PPTC thermistor in order to accelerate heat rise to the switching temperature, TS. While the foregoing patents show combinations of semiconductor devices and PPTC thermistor devices in thermal contact, those patents do not show or suggest inclusion of fully integrated over-voltage/over-current circuit protection elements inside standardized and highly miniaturized connector sockets, such as a Micro-B USB connector socket.
Miniaturized electrical connectors including connector sockets that conform to a standardized specification are constrained by size requirements and pin configurations such that it becomes difficult to include any additional electrical components, elements or devices within the size requirements and still maintain conformance with the standard connector/socket specification.